Xmr angle sensors

ABSTRACT

Embodiments relate to xMR sensors, in particular AMR and/or TMR angle sensors with an angle range of 360 degrees. In embodiments, AMR angle sensors with a range of 360 degrees combine conventional, highly accurate AMR angle structures with structures in which an AMR layer is continuously magnetically biased by an exchange bias coupling effect. The equivalent bias field is lower than the external rotating magnetic field and is applied continuously to separate sensor structures. Thus, in contrast with conventional solutions, no temporary, auxiliary magnetic field need be generated, and embodiments are suitable for magnetic fields up to about 100 mT or more. Additional embodiments relate to combined TMR and AMR structures. In such embodiments, a TMR stack with a free layer functioning as an AMR structure is used. With a single such stack, contacted in different modes, a high-precision angle sensor with 360 degrees of uniqueness can be realized.

TECHNICAL FIELD

The invention relates generally to integrated circuit (IC) sensors andmore particularly to magnetoresistive IC angle sensors having 360-degreeuniqueness.

BACKGROUND

Magnetoresistive sensors can include anisotropic magnetoresistive (AMR),giant magnetoresistive (GMR), tunnel magnetoresistive (TMR) and othertechnologies, referred to collectively as xMR technologies. XMR sensorscan be used for a variety of applications, including magnetic field andcurrent sensors, speed sensors, rotation sensors and angle sensors,among others.

Conventional AMR angle sensors are inherently limited to an angleuniqueness of 180 degrees due to the 90-degree uniqueness of the AMReffect with respect to a rotating external in-plane field. Thus, thereare many applications for angle sensors with greater than 180-degreerange that are instead fulfilled by angle sensors based on GMR or TMRtechnology. These technologies, however, suffer from considerableaccuracy drift, especially at high magnetic fields in combination withhigh temperatures, which prevents GMR usage in applications with highaccuracy requirements. Because AMR technology exhibits no magnetic fielddependent accuracy drift, it is typically the preferred technologychoice for very high accuracy applications.

Solutions exist that attempt to extend the range of AMR angle sensors to360 degrees. For example, some increase the anisotropic field strengthusing an additional device, such as an integrated coil or hard magneticbias layer. Such solutions often require that the external magneticfield be lower than the sensor anisotropy field strength, though, whichlimits the usually desired high magnetic fields. Other solutions applyan additional, or “auxiliary,” magnetic field, such as by integratedcoils, which can be lower than the external magnetic field in order toallow the film magnetization to rotate. Drawbacks of these solutions,however, include increased power consumption and limited maximummeasuring field, as well as increased measuring time due to theapplication of the temporary auxiliary field.

Therefore, a need remains for improved xMR sensors, including an AMRsensor having a 360-degree range.

SUMMARY

Embodiments relate to xMR sensors, sensor elements and structures, andmethods, including AMR and/or TMR angle sensors having 360-degreeranges.

In an embodiment, An anisotropic magnetoresistive (AMR) angle sensor formeasuring an external magnetic field with 360 degrees of uniquenesscomprises a first AMR sensor element; and a second AMR sensor elementwhich, in operation, is continuously biased with a bias magnetic field,the bias magnetic field being smaller than the external magnetic field.

In an embodiment, a method of determining a measured magnetic fieldangle having 360-degree uniqueness comprises providing an anisotropicmagnetoresistive (AMR) angle sensor comprising first, second and thirdAMR sensor element arrangements, wherein AMR layers in the first AMRsensor element arrangement are exchange biased in a direction that isrotated with respect to a direction of exchange bias of AMR layers inthe third AMR sensor element arrangement; measuring a first magneticfield angle by the second AMR sensor element arrangement; measuringsecond and third magnetic field angles by the first and third AMR sensorelement arrangement, respectively; determining a first differencebetween the first and second magnetic field angles and a seconddifference between the first and third magnetic field angles;determining an arctan (ATAN) of a ratio of the first difference to thesecond difference; and determining a measured magnetic field anglehaving 360-degree uniqueness from the ATAN.

In an embodiment, a method of determining a measured magnetic fieldangle having 360-degree uniqueness comprises providing an anisotropicmagnetoresistive (AMR) angle sensor comprising first, second and thirdAMR sensor element arrangements, wherein AMR layers in the first AMRsensor element arrangement are exchange biased in a direction that isrotated with respect to a direction of exchange bias of AMR layers inthe third AMR sensor element arrangement; measuring a first magneticfield angle by the second AMR sensor element arrangement; measuring asecond magnetic field angle by the first AMR sensor element arrangement;determining a first difference between the first and second magneticfield angles; determining a measured magnetic field angle having360-degree uniqueness from the arctan (ATAN) according to the following:if the first magnetic field angle is greater than an angle B or if thefirst magnetic field angle is less than 180 degrees minus angle B, thenthe measured magnetic field angle is equal to the first magnetic fieldangle if the first difference is greater than 0, or the first magneticfield angle plus 180 degrees if the first difference is less than 0; andif the first magnetic field angle is less than the angle B or if thefirst magnetic field angle is greater than 180 degrees minus angle B,then measure a third magnetic field angle by the third AMR sensorelement arrangement, calculate an ATAN of a ratio of the first and thirdmagnetic field angles, if the ATAN minus 180 degrees is less than thefirst magnetic field angle, then the measured magnetic field angle isequal to the first magnetic field angle, and if the ATAN minus 180degrees is greater than or equal to the first magnetic field angle, thenthe measured magnetic field angle is equal to the first magnetic fieldangle plus 180 degrees; where the angle B is an assumed absolute valueof a deviation of orthogonality.

In an embodiment, an angle sensor for measuring an external magneticfield with 360 degrees of uniqueness comprises a tunnelingmagnetoresistive (TMR) stack having a tunneling barrier layer, a layerexhibiting an anisotropic magnetoresistive (AMR) effect and a firstelectrode on a first side of the tunneling barrier layer, a secondelectrode on a second side of the tunneling barrier layer, and first andsecond contact sets on the first side of the tunneling barrier, whereinthe first electrode exhibits an AMR effect; wherein the TMR stack has afirst sensor configuration when the first contact set is used and asecond sensor configuration when the second contact set is used, thefirst and second contact sets having different contact distances.

In an embodiment, a method of determining a measured magnetic fieldangle having 360-degree uniqueness comprises providing a tunnelingmagnetoresistive (TMR) stack having a tunneling barrier layer, a layerexhibiting an anisotropic magnetoresistive (AMR) effect and a firstelectrode on a first side of the tunneling barrier layer, a secondelectrode on a second side of the tunneling barrier layer, and first andsecond contact sets on the first side of the tunneling barrier, whereinthe first electrode exhibits an AMR effect; accessing a first sensorconfiguration of the TMR stack by the first contact set to measure acurrent-in-plane (CIP) TMR effect; accessing a second sensorconfiguration of the TMR stack by the second contact set to measure anAMR effect, the second contact set having a contact distance smallerthan a contact distance of the first contact set; and using the CIP TMReffect and AMR effect to determine a 360-degree unique magnetic fieldangle.

In an embodiment, an angle sensor for measuring an external magneticfield with 360 degrees of uniqueness comprises a tunnelingmagnetoresistive (TMR) stack having a tunneling barrier layer, a layerexhibiting an anisotropic magnetoresistive (AMR) effect and a firstelectrode on a first side of the tunneling barrier layer, a secondelectrode on a second side of the tunneling barrier layer, a firstcontact set comprising contacts on the first and second sides of thetunneling barrier layer, and a second contact set on the first side ofthe tunneling barrier layer, wherein the first electrode exhibits an AMReffect; wherein the TMR stack has a first sensor configuration when thefirst contact set is used and a second sensor configuration when thesecond contact set is used, the first and second contact sets havingdifferent contact distances

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1A is an angle diagram according to an embodiment.

FIG. 1B is an angle diagram according to an embodiment.

FIG. 1C is an angle diagram according to an embodiment.

FIG. 2 is a block diagram of an AMR sensor configuration according to anembodiment.

FIG. 3A is a block diagram of an AMR stack according to an embodiment.

FIG. 3B is a block diagram of an AMR stack according to an embodiment.

FIG. 4 is a block diagram sequence of a damascene process according toan embodiment.

FIG. 5 is a block diagram of an AMR stack according to an embodiment.

FIG. 6A is a side view block diagram of an AMR stack according to anembodiment.

FIG. 6B is a top view block diagram of an AMR stack according to anembodiment.

FIG. 7A is a block diagram of an AMR stripe according to an embodiment.

FIG. 7B is a block diagram of AMR stripes according to an embodiment.

FIG. 8 is a flow chart of a process according to an embodiment.

FIG. 9 is a simulated plot of angle difference versus magnetic fieldangle according to an embodiment.

FIG. 10 is a flow chart of a process according to an embodiment.

FIG. 11 is a block diagram of a TMR stack according to an embodiment.

FIG. 12 is an equivalent circuit diagram of the stack of FIG. 11.

FIG. 13 is a simulated plot of CIP ratio of CPP TMR versus contactdistance according to an embodiment.

FIG. 14 is a simulated plot of CIP ratio of CPP TMR versus contactdistance according to an embodiment.

FIG. 15 is a TMR stack according to an embodiment.

FIG. 16 is a simulated plot of CIP ratio of CPP TMR versus contactdistance according to an embodiment.

FIG. 17 is a simulated plot of CIP ratio of CPP TMR versus contactdistance according to an embodiment.

FIG. 18 is a simulated plot of angle error versus magnetic field angleaccording to an embodiment.

FIG. 19 is a simulated plot of angle error versus magnetic field angleaccording to an embodiment.

FIG. 20 is a block diagram of a TMR sensor structure according to anembodiment.

FIG. 21 is a block diagram of a sensor structure according to anembodiment.

FIG. 22 is a block diagram of a sensor structure according to anembodiment.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Embodiments relate to xMR sensors, in particular AMR angle sensors withan angle range of 360 degrees. In embodiments, AMR angle sensors with arange of 360 degrees combine conventional, highly accurate AMR anglestructures with structures in which an AMR layer is continuouslymagnetically biased by an exchange bias coupling effect. The equivalentbias field is lower than the external rotating magnetic field and isapplied continuously to separate sensor structures. Thus, in contrastwith conventional solutions, no temporary, auxiliary magnetic fieldneeds to be generated, and embodiments are suitable for magnetic fieldsup to about 100 mT or more. Additional embodiments relate to combinedTMR and AMR structures. In such embodiments, a TMR stack with a freelayer functioning as an AMR structure is used. With a single such stack,contacted in different modes, a high-precision angle sensor with 360degrees of uniqueness can be realized.

The angle range of a conventional AMR angle sensor is depictedschematically in FIG. 1A. Because of the 90-degree uniqueness of asingle AMR element signal, half-spaces of the signal (i.e., φ vs. φ+180in the example of FIG. 1A) cannot be distinguished.

If a comparatively low auxiliary magnetic field in the y-direction isapplied, however, the magnetization of the AMR film varies slightly, asdepicted by Δ in FIG. 1B. The measured angle thereby increases to φ+Δ ifthe actual angle of the external field is φ and decreases by Δ if theactual angle is φ+180.

If the external field is 90 degrees or 270 degrees, however, anauxiliary bias field in the x-direction can be applied, as depicted inFIG. 1C. The measured angle of a magnetic field in the +y direction willthereby be lowered, with a field in the −y direction enhanced. As aresult, left and right half-spaces (as oriented in FIG. 1C) can bedistinguished.

In contrast with conventional solutions, however, it is desired toachieve the bias fields on-chip permanently, rather than through coilsor additional devices that apply temporary fields, and for the fields tohave lower field strength than the external magnetic field. Inembodiments, additional sensor structures are provided such that the AMRlayer is directly magnetically coupled to a hard magnetic structure bythe so-called exchange bias effect. The magnetization direction of thehard magnetic structure can be adjusted, as discussed herein below. Inorder to be able to evaluate the 360-degree unique signal regardless ofexternal magnetic field direction, two additional Wheatstone bridgeswith different exchange bias directions are added to a conventionalconfiguration in embodiments. The coupling field is smaller than theexternal rotating magnetic field in order to enable a rotation of theAMR magnetization.

Referring to FIG. 2, a sensor configuration according to an embodimentis depicted. Sensor 100 comprises a Wheatstone bridge portion 102 of aconventional AMR angle sensor having 180 degrees of uniqueness. Portion102 comprises two full bridges rotated by 45 degrees with respect to oneanother, with the illustrated double arrows indicating the main currentflow axis. Sensor 100 also comprises two additional Wheatstone fullbridges 104 and 106, in which the AMR layers are magnetically coupled toa certain direction of exchange bias field indicated by the block-stylearrows. In the embodiment of FIG. 2, the directions are 0 degrees and 90degrees to form full bridges 104 and 106. The addition of bridges 104and 106 increases active area; half-bridges with fixed, not magneticallyactive reference resistances can be used in other embodiments to reducethe added active area. Further, if 360-degree measurement is not neededat all times in some applications, exchange biased bridges 104 and 106can be switched off from the supply Vdd to reduce power consumption.

In other embodiments, the angles of rotation can vary from the 45degrees illustrated in FIG. 2. In general, however, the angles are notorthogonal. For example, the exchange biasing directions of the AMRportions of sensor 100 can be rotated by some degree in a range of 0 to90 degrees or in a range of 90 to 180 degrees, in various embodiments.Resulting non-orthogonality can be compensated for by a calibration stepduring sensor production.

The exchange bias effect has been used in GMR and TMR technologies tobuild a stable reference magnetization system in so-called “spin-valve”stack types. Referring to FIG. 3A, a natural anti-ferromagnetic layer(NAF) is coupled to a layer exhibiting an AMR effect, or an AMR layer.In FIG. 3B, a ferromagnetic (FM) layer, such as cobalt iron (CoFe) ornickel iron (NiFe), is in direct contact with an NAF, such as platinummanganese (PtMn), nickel manganese (NiMn) or iridium manganese (IrMn).Heating and cooling of the stack in a magnetic field leads to hardmagnetization in the direction of the magnetic field through theexchange bias effect between the FM and the NAF. This same configurationcan be used for the exchange biased AMR layer, with tuning of theexchange bias field strength possible in a restricted range by varyingthe NAF material, the thickness of the NAF layer or the AMR layerthickness. In embodiments, the AMR layer is comparatively thick, such asabout 20 to about 30 nanometers (nm) and exhibits a significant magneticmoment that can lead to reasonable thermo-magnetic drift of the exchangebias field direction.

In FIG. 3B, the FM layer is in direction contact with the NAF layer. TheFM layer thickness can be chosen to be only as thick as necessary tobuild a significant exchange bias and at the same time a minimummagnetic moment. Next to the FM layer is a non-magnetic coupling layer(NML), such as ruthenium (Ru). The thickness of the NML defines thecoupling strength and sign, i.e. if the coupling is ferromagnetic oranti-ferromagnetic, between the exchange biased FM layer and the AMRlayer on the side of the NML by the so-calledRuderman-Kittel-Kasuya-Yosida (RKKY)-exchange coupling. As a result, theeffective bias field for the AMR layer can be tailored in a wide rangeby varying the NML thickness in embodiments. Furthermore, the directionof the imprinted exchange bias field is most stable, since the thin FMlayer exhibits a minimum magnetic moment to be tilted in an externalmagnetic field.

The following will describe one way of processing structures with andwithout exchange biased AMR layers next to each other, in accordancewith various embodiments. AMR relevant layers can be deposited in twosteps, including a damascene process such as is described in co-pendingU.S. application Ser. No. 12/946,460 entitled “XMR SENSORS WITH HIGHSHAPE ANISOTROPY” and which is incorporated herein by reference in itsentirety. One example according to an embodiment will be described withrespect to FIG. 4. Embodiments can include more or fewer steps thanspecifically illustrated, as understood by one skilled in the art; forexample, a lithography process can occur between (a) and (b) but is notdepicted.

At (a), a thin dielectric 120 is applied to a substrate 118. In anembodiment, substrate 118 has a polished surface on which dielectric 120is applied and includes two vias 122 for later providing a connection toan underlying wiring metal. In embodiments, dielectric 120 comprisessilicon nitride or oxide and is applied with a thickness approximatelyequal to that desired for exchange bias layer 103. Other suitabledielectric materials can be used in other embodiments. As depicted, vias122 are plugged with tungsten during processing.

At (b), a groove 124 having the desired geometry of exchange bias layer103 is etched into dielectric 120 with a high selectivity to theunderlying oxide of substrate 118. In embodiments, a width of groove 124is in a range of about 100 nm to about 10 μm, or smaller than the AMRstructure.

At (c), exchange bias layer 103 is deposited. Exchange bias layer 103 asdeposited can include a seed layer, a natural antiferromagnet layer andoptional additional functional layers in embodiments; see, for example,FIGS. 3A and 3B.

At (d), a chemical-mechanical polishing (CMP) process removes theportions of exchange bias layer 103 on dielectric 120. Exchange biaslayer 103 remains in former groove 124.

At (e), remaining stack 111 is deposited. In an embodiment, remainingstack 111 has been structured by a standard etch process, such as achemical, plasma or sputter etch process, the dimensions of remainingstack 111 being relaxed relative to those of exchange bias layer 103,and is deposited after a conditioning process is carried out on polishedexchange bias layer 103.

As a result, there are regions with and without the exchange biased AMRlayer. Other methodologies, including those also discussed in theaforementioned co-pending application, can also be used in embodiments.

In another example, and referring to FIG. 5, the AMR structures with andwithout exchange biasing are stacked and deposited in a single step,separated by an insulator layer, such as aluminum oxide (Al2O3) ormagnesium oxide (MgO). An additional wiring layer is introduced toprovide contact from both sides of the stack, but active area can alsobe significantly reduced.

Two different directions of exchange bias magnetization also are to beimprinted. A first option for doing so is to use laser-aided localheating of the exchange biased AMR structures in a magnetic field. Sucha process is conventionally used for GMR angle sensor processing, suchas is described in co-owned U.S. Pat. No. 7,678,585, which isincorporated herein by reference. A drawback of this process, however,is that each sensor resistance is processed individually, which takesadditional time.

Another example option involves processing the different magnetizationssimultaneously for the whole wafer, such as is described in co-ownedU.S. Patent Application Pub. No. 2010/0118447, which is incorporatedherein by reference. Basically, a first orientation for all exchangebiased structures is imposed in a wafer-level magnetization step. In asecond non-magnetic anneal, the exchange bias direction is tiltedaccording to the shape selected for the exchange bias system part of theAMR sensor, in other words for the shape anisotropy effect. The shapeanisotropy is chosen to be different for the two exchange biasdirections. Referring to FIGS. 6A and 6B, shape anisotropy can beachieved even if wide AMR sensor structures are used. The exchange biassection 602 is not homogeneous beneath the AMR layer 604 but rather isdivided in several narrow portions, i.e., not all regions of AMR layer604 are exchange biased coupled. This effects a weakening of theeffective exchange bias coupling and should be considered when tailoringthe exchange bias strength.

Referring to FIG. 7A, the influence of the structure orientation on areorientation of the pinned layer magnetization after a thermaltreatment is illustrated. Assuming that there is an angle of 90degrees-β between the stripe length axis (shape) and the initial pinnedlayer magnetization, a thermal treatment with temperatures near theso-called “blocking” temperature of the system will lead to tilt of themagnetization by an angle α. A proper configuration of the two types ofgeometries for the pinned layer system will lead to an angle of 2αbetween the pinned layer magnetization. FIG. 7B illustrates generationof the two different pinned layer orientations by the geometry.

Returning to the aforementioned challenge of determining 360-degreeuniqueness in conventional AMR angle sensors, embodiments discussedherein provide a multitude of possibilities for determining 360-degreeuniqueness. A first approach includes implementing additional CORDIC(COrdinate Rotation DIgital Computer) calculations without making anyassumptions, as illustrated in FIG. 8 with reference to FIG. 2.

At 802, the magnetic field angle α1 is measured by sensor portion 102.At 804, magnetic field angles α2 and α3 are measured by sensor parts 106and 104, respectively. In an embodiment, 804 is carried out at the sametime as 802. At 806, measured angle differences are calculated:α1−α2=Δα2 and α1−α3=Δα3. The result is a sine- and cosine-likecharacteristic (refer, for example, to the simulated results of FIG. 9)that can be used to determine 360-degree uniqueness. Thus, at 808, thearctan (ATAN) of (Δα2/Δα3) is determined for ΦΔ. If ΦΔ−180 degrees isless than α1, then the actual angle, α, is α1; if ΦΔ−180 degrees isgreater than or equal to Δ1, then α is α1+180 degrees.

Another method for determining α with 360-degree uniqueness with feweradditional CORDIC calculations but an assumption of a misalignment ofthe two orthogonal exchange bias directions is depicted in FIG. 10 withreference to FIG. 2. This process takes advantage of the fact that thehalf-space is clearly defined by the value Δα2 except at or around thezero crossings (e.g., 0 and 180 degrees under ideal conditions).

At 1002, the magnetic field angle α1 is measured by sensor portion 102.At 1004, magnetic field angle α2 is measured by sensor portion 106. Inan embodiment, 1004 is carried out at the same time as 1002. At 1006,the measured angle difference is calculated: α1−α2=Δα2. At 1008, anassumption is made that the absolute value of the orthogonality deviatesby an angle βo. Then, at 1010, the real angle, α, is calculated. At1012, if ((α1>βo) or (α1<(180−βo)), then: if (ΦΔ>0), then α=α1, or if(ΦΔ<0), then α=α1+180. At 1014, if ((α1<βo) or (α>(180−βo)), then at1016, α3 is measured by sensor portion 104. At 1018, the ATAN of(Δα2/Δα3) is determined for ΦΔ. If ΦΔ−180 degrees is less than α1, thenthe actual angle, α, is α1; if ΦΔ−180 degrees is greater than or equalto Δ1, then Δ is Δ1+180 degrees.

Accurate alignment of the two exchange bias direction with respect toone another or to the basic current directions is not necessary, as longas the directions are defined within an 180-degree accuracy. Therefore,a realistic drift of the exchange bias directions during sensor lifetimedoes not affect the 360-degree recognition.

Embodiments thus relate to AMR angle sensors which couple the AMR layerto the pinned layer in order to effect 360-degree uniqueness. Aspreviously mentioned, however, the desired half-space information couldbe provided by a GMR or TMR spin-valve sensor structure, whichinherently can provide a 360-degree unique signal angle. As alsopreviously mentioned, there are inherent advantages to AMR sensorsstructures that make them desirable for at least some applications.Thus, further embodiments aim to take advantage of simultaneous AMR andTMR effects by including a TMR structure in a current-in-plane (CIP)configuration to accomplish the same or similar 360-degree uniquenesseffects.

Referring to FIG. 11, a TMR stack 1100 can be described as top andbottom electrodes separated by a tunnel barrier, resulting in anequivalent circuit as depicted in FIG. 12. When a voltage is applied tothe terminal contacts, a voltage gradient over the barrier also exists,giving rise to a TMR signal that is lower than the maximum possiblesignal for a conventional current-perpendicular-to-plane (CPP) mode dueto a shunting current through the top and bottom electrodes.

As mentioned above, embodiments utilize TMR structures in CIPconfigurations. Referring to FIG. 13, there are two main influencingfactors of CIP signals: an optimum contact distance with a maximum CIPTMR signal, and the ratio of top and bottom resistance values. Regardingthe former, for lower distances, the bottom electrode shortens the wholestack and only a small amount of current flows through the barriers. Forlarger contact distances, the element resistance is mainly determined bythe parallel resistance of the top and bottom electrodes and dominatesthe resistance change by the TMR effect.

Regarding the second factor, in order to get as much current as possiblethrough the barrier (i.e., a high signal), the bottom electrode shouldexhibit a high resistance (R_(B)), the top electrode a low resistance(R_(T)). The achievable CIP ratio of the maximum CPP signalsignificantly increases with a rising R_(B)/R_(T) ratio. The resistanceof the barrier has no major influence on the signal height but on thedistance value for the optimum signal height: the higher the barrierresistance, the wider the contacts for an optimum CIP TMR effect. Referto FIG. 14.

The strong influence of the contact distance on the current distributionthrough the TMR stack can be used to make either only the bottomelectrode or the whole stack measureable. According to embodiments, theTMR stack is provided with a layer exhibiting an AMR effect, such as apermalloy layer. This layer can be about 15 to about 30 nm thick inembodiments and can comprise, for example, NiFe, which per se exhibitsan AMR effect, such as about 3% (dR/R) in an embodiment. An example TMRspin-valve stack 1500 is depicted in FIG. 15, in which the permalloylayer of NiFe in an embodiment acts as the free layer. The contacts arelocated on the free layer side. For small contact distances, the currentmainly flows through the bottom electrode, the electrode located at thecontact side (i.e., through the AMR layer). Consequently, only themagnetic properties of the bottom electrode, the layer with the AMReffect, can be observed. Referring again to FIG. 13, the TMR effect canbe suppressed, depending on the stack design, and a high-precision180-degree angle sensor is obtained. At elevated contact distances, amaximum CIP TMR effect can be measured. If the CIP TMR effect is higherthan the AMR effect or if the AMR effect can be suppressed by certainmeasures, a 360-degree unique angle signal can be detected. As a result,and according to embodiments, a high precision AMR angle signal and360-degree information can be obtained with the same stack by choosingadapted contact distances.

FIG. 16 depicts the results of a two-dimensional numerical simulationfor the CIP signal versus contact distance behavior of an exemplary TMRstack with, as in one example embodiment, a 20 nm NiFe free layer, a 1nm reference layer, a 2 nm pinned layer and a 15 nm naturalantiferromagnet material such as PtMn. With increasing barrierresistance, the CIP TMR signal can be drastically reduced in the smallcontact distance region. For example, FIG. 17 shows, for typical barrierlayer resistance of Rbarr=10̂7 Ωμm̂2 and a contact distance of 7 μm, a CIPTMR ratio of the CPP TMR signal of 10̂−3%. Assuming a CPP TMR effect ofabout 100%, the remaining CIP TMR signal is then 10̂−3%. With an AMReffect of about 3%, the overall signal of the structure is clearlydominated by the AMR signal of the free layer. An evaluation of the AMRsignal slightly modulated with the residual CIP TMR signal underaforementioned conditions results in an additional angular error(maximum) 0.01 degrees, which is almost negligible. Refer to FIG. 18.This means that, even with the disturbing TMR signal, a high-precisionAMR angle signal is obtained.

Relatedly, the necessary small contact distance of about 10 μm in anembodiment works quite well with the concept of a high-precision AMRangle sensor as disclosed in co-pending and co-owned U.S. applicationSer. No. 12/950,456, incorporated herein by reference in it entirety andwhich discusses a series connection of single circular elements with adiameter of about 10 μm in an embodiment.

In embodiments having contact distances of greater than 200 μm, such asabout 700 μm, a CIP TMR signal of greater than about 4% is expected,which is higher than the unwanted remaining AMR effect of about 3%previously discussed. FIG. 19 depicts an additional angle error by theAMR signal modulated CIP TMR signal of about 50 degrees, which is stillsufficient because only 180-degree accuracy is required in order toobtain the correct half-space information.

Nevertheless, it is possible to almost completely suppress the unwantedAMR effect for the structures in which the CIP TMR effect is extractedby combining elements with orthogonal current directions; then the AMReffect cancels out. In this case, no additional error has to be takeninto account for the CIP TMR structure. Another possibility is the usageof an extended plate with point contact areas along a line, resulting ina wide current direction distribution; such a structure does not show areasonable AMR effect. An alternative option is to choose the largercontact distance to measure the AMR effect. Referring again to FIG. 16,a decrease of the CIP TMR signal can be seen for larger contactdistances and smaller barrier resistances.

Therefore, sensor embodiments can comprise two types of angle sensorstructures: one with a small contact distance, one with a widerdistance. As a result, one measures only the AMR effect of the freelayer (high precision 180-degree unique angle signal), the othermeasures only the CIP TMR effect (low precision 360-degree unique anglesignal) taking into account measuring for the AMR effect suppression. Incontrast with pure GMR/TMR angle sensors, the reference system of thestack does not need to be especially stable; an accuracy drift ofseveral 10-degrees can be tolerated as the absolute accuracy need onlybe less than about 180 degrees. As a result, a sensor structureaccording to embodiments can provide a high precision angular accuracyeven for high temperatures and external magnetic fields, such as up toabout 100 mT, which providing the advantages of a single stack and noadditional GMR processing.

Thus, and referring to FIG. 20, a Wheatstone bridge configuration 2000according to an embodiment is depicted. Bridge configuration 2000 is anexample TMR angle sensor component comprising two full Wheatstonebridges 2002 and 2004. Arrows indicate the magnetization direction ofthe reference magnetization of the TMR spin-valve stack. The necessarylocal definition of the reference magnetization direction can beachieved, for example, by a laser magnetization process as previouslydiscussed herein. Within each full bridge 2002 and 2004, themagnetization directions are aligned anti-parallel; between the two fullbridges 2002 and 2004 the direction are rotated by 90 degrees.

A sensor structure 2100 according to an embodiment is depicted in FIG.21. Sensor 2100 comprises full Wheatstone bridges 2102 and 2104 withsingle resistances, each comprising a series connection ofcircular-shaped structures with defined contact areas, wherein thecontact distance is small to suppress the CIP TMR signal of the stack.Here, the contact distance of each resistor is high enough to exhibit asignificant CIP TMR effect. Furthermore, a meander structure withorthogonal current orientation is chosen to reduce the AMR signalinfluence on the CIP TMR signal. The arrows in the CIP TMR portion 2106indicate the locally imprinted magnetization directions. In embodiments,CIP TMR portion 2106 can be designed as a half-bridge in order to reducecurrent consumption and active area. Additionally, there is no need fora wide stripe width, since a low angular error for CIP TMR portion 2106is not mandatory; it is only needed to determine the half-space of theexternal magnetic field, thus only 180-degree accuracy is required.Furthermore, CIP TMR portion 2106 can be switched on or off by switchesin embodiments in order to be activated only at the beginning of sensoroperation for current-saving purposes.

FIG. 22 depicts an advantageous bridge layout 2200 having a seriesconnection of single circular sensor elements, with eight resistances(A, B, C, D, E, F, G and H) included. The entire bridge 2200 is designedin a circular structure, which minimizes the active area at certainresistances. As a consequence, the additional angular errors caused bydisplacements of the external magnet in the system can be reduced.

It should also be noted that the TMR sensor portion can be operated inthe customary TMR current-perpendicular-to-plane CPP configuration. Insuch embodiments, contacts on the second side of the tunneling barrierare also included, in addition to the contacts on the first side of thetunneling barrier.

Embodiments thus relate to xMR sensors, in particular AMR angle sensorswith an angle range of 360 degrees. In embodiments, AMR angle sensorswith a range of 360 degrees combine conventional, highly accurate AMRangle structures with structures in which an AMR layer is continuouslymagnetically biased by an exchange bias coupling effect. The equivalentbias field is lower than the external rotating magnetic field and isapplied continuously to separate sensor structures. Thus, in contrastwith conventional solutions, no temporary, auxiliary magnetic field needbe generated, and embodiments are suitable for magnetic fields up toabout 100 mT or more. Additional embodiments relate to combined TMR andAMR structures. In such embodiments, a TMR stack with a thick permalloyfree layer, functioning as an AMR structure, is used. With a single suchstack, contacted in different modes, a high-precision angle sensor with360 degrees of uniqueness can be realized.

Various embodiments of systems, devices and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the invention. It should be appreciated,moreover, that the various features of the embodiments that have beendescribed as well as of the claims may be combined in various ways toproduce numerous additional embodiments. Moreover, while variousmaterials, dimensions, shapes, implantation locations, etc. have beendescribed for use with disclosed embodiments, others besides thosedisclosed may be utilized without exceeding the scope of the invention.

Persons of ordinary skill in the relevant arts will recognize that theinvention may comprise fewer features than illustrated in any individualembodiment described above. The embodiments described herein are notmeant to be an exhaustive presentation of the ways in which the variousfeatures of the invention may be combined. Accordingly, the embodimentsare not mutually exclusive combinations of features; rather, theinvention may comprise a combination of different individual featuresselected from different individual embodiments and/or from differentclaims, as understood by persons of ordinary skill in the art.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

For purposes of interpreting the claims for the present invention, it isexpressly intended that the provisions of Section 112, sixth paragraphof 35 U.S.C. are not to be invoked unless the specific terms “means for”or “step for” are recited in a claim.

1. An anisotropic magnetoresistive (AMR) angle sensor for measuring anexternal magnetic field with 360 degrees of uniqueness comprising: afirst AMR sensor element; and a second AMR sensor element which, inoperation, is continuously biased with a bias magnetic field, the biasmagnetic field being smaller than the external magnetic field.
 2. TheAMR angle sensor of claim 1, wherein the bias magnetic field is providedby an exchange bias effect on the second AMR sensor element.
 3. The AMRangle sensor of claim 2, wherein the exchange bias effect is created bycoupling an AMR layer of the second AMR sensor element to anantiferromagnetic layer.
 4. The AMR angle sensor of claim 3, wherein theAMR layer comprises a material selected from the group consisting ofcobalt iron (CoFe) and nickel iron (NiFe).
 5. The AMR angle sensor ofclaim 3, wherein the antiferromagnetic layer comprises a materialselected from the group consisting of platinum manganese (PtMn), nickelmanganese (NiMn) and iridium manganese (IrMn).
 6. The AMR angle sensorof claim 3, wherein the AMR layer has a thickness in a range of about 10nm to about 30 nm.
 7. The AMR angle sensor of claim 3, wherein the AMRlayer is coupled to the antiferromagnetic layer by at least one offerromagnetic layer and a non-magnetic coupling layer.
 8. The AMR anglesensor of claim 7, wherein the non-magnetic coupling layer comprises Ru.9. A method of determining a measured magnetic field angle having360-degree uniqueness comprising: providing an anisotropicmagnetoresistive (AMR) angle sensor comprising first, second and thirdAMR sensor element arrangements, wherein AMR layers in the first AMRsensor element arrangement are exchange biased in a direction that isrotated with respect to a direction of exchange bias of AMR layers inthe third AMR sensor element arrangement; measuring a first magneticfield angle by the second AMR sensor element arrangement; measuringsecond and third magnetic field angles by the first and third AMR sensorelement arrangement, respectively; determining a first differencebetween the first and second magnetic field angles and a seconddifference between the first and third magnetic field angles;determining an arctan (ATAN) of a ratio of the first difference to thesecond difference; and determining a measured magnetic field anglehaving 360-degree uniqueness from the ATAN.
 10. The method of claim 9,wherein determining a magnetic field angle having 360-degree uniquenessfrom the ATAN further comprises: if the ATAN minus 180 degrees is lessthan the first magnetic field angle, then the measured magnetic fieldangle is equal to the first magnetic field angle; and if the ATAN minus180 degrees is greater than or equal to the first magnetic field angle,then the measured magnetic field angle is equal to the first magneticfield angle plus 180 degrees.
 11. The method of claim 9, wherein thefirst, second and third AMR sensor element arrangements comprise fullWheatstone bridges.
 12. The method of claim 9, wherein the directions ofexchange bias of the first and third sensor element arrangements arerotated with respect to another by about 90 degrees.
 13. The method ofclaim 9, wherein the directions of exchange bias of the first and thirdsensor element arrangements are rotated with respect to another in arange of about 0 degrees to about 90 degrees or in a range of about 90degrees to about 180 degrees.
 14. A method of determining a measuredmagnetic field angle having 360-degree uniqueness comprising: providingan anisotropic magnetoresistive (AMR) angle sensor comprising first,second and third AMR sensor element arrangements, wherein AMR layers inthe first AMR sensor element arrangement are exchange biased in adirection that is rotated with respect to a direction of exchange biasof AMR layers in the third AMR sensor element arrangement; measuring afirst magnetic field angle by the second AMR sensor element arrangement;measuring a second magnetic field angle by the first AMR sensor elementarrangement; determining a first difference between the first and secondmagnetic field angles; determining a measured magnetic field anglehaving 360-degree uniqueness from the arctan (ATAN) according to thefollowing: if the first magnetic field angle is greater than an angle Bor if the first magnetic field angle is less than 180 degrees minusangle B, then the measured magnetic field angle is equal to the firstmagnetic field angle if the first difference is greater than 0, or thefirst magnetic field angle plus 180 degrees if the first difference isless than 0; and if the first magnetic field angle is less than theangle B or if the first magnetic field angle is greater than 180 degreesminus angle B, then measure a third magnetic field angle by the thirdAMR sensor element arrangement, calculate an ATAN of a ratio of thefirst and third magnetic field angles, if the ATAN minus 180 degrees isless than the first magnetic field angle, then the measured magneticfield angle is equal to the first magnetic field angle, and if the ATANminus 180 degrees is greater than or equal to the first magnetic fieldangle, then the measured magnetic field angle is equal to the firstmagnetic field angle plus 180 degrees; where the angle B is an assumedabsolute value of a deviation of orthogonality.
 15. The method of claim14, wherein the first, second and third AMR sensor element arrangementscomprise full Wheatstone bridges.
 16. An angle sensor for measuring anexternal magnetic field with 360 degrees of uniqueness comprising: atunneling magnetoresistive (TMR) stack having a tunneling barrier layer,a layer exhibiting an anisotropic magnetoresistive (AMR) effect and afirst electrode on a first side of the tunneling barrier layer, a secondelectrode on a second side of the tunneling barrier layer, and first andsecond contact sets on the first side of the tunneling barrier, whereinthe first electrode exhibits an AMR effect; wherein the TMR stack has afirst sensor configuration when the first contact set is used and asecond sensor configuration when the second contact set is used, thefirst and second contact sets having different contact distances. 17.The angle sensor of claim 16, wherein the TMR stack comprises acurrent-in-plane (CIP) configuration.
 18. The angle sensor of claim 16,wherein the layer exhibiting an AMR effect is a free layer.
 19. Theangle sensor of claim 16, wherein the layer exhibiting an AMR effectcomprises at least one of nickel (Ni), iron (Fe) or cobalt (Co) or analloy thereof.
 20. The angle sensor of claim 16, wherein the layerexhibiting an AMR effect comprises permalloy.
 21. The angle sensor ofclaim 16, wherein the first contact distance is greater than the secondcontact distance.
 22. The angle sensor of claim 16, wherein the firstcontact distance is about an order of magnitude greater than the secondcontact distance.
 23. The angle sensor of claim 22, wherein the firstcontact distance is equal to or greater than about 200 μm and the secondcontact distance is equal to or less than about 10 μm.
 24. The anglesensor of claim 16, wherein the first sensor configuration measures acurrent-in-plane (CIP) TMR effect and the second sensor configurationmeasures an AMR effect.
 25. The angle sensor of claim 24, wherein thefirst sensor configuration is configured to provide orthogonal currentdirections to aid suppression of the AMR effect.
 26. The angle sensor ofclaim 16, wherein the TMR angle sensor provides a 360-degree uniqueoutput signal.
 27. A method of determining a measured magnetic fieldangle having 360-degree uniqueness comprising: providing a tunnelingmagnetoresistive (TMR) stack having a tunneling barrier layer, a layerexhibiting an anisotropic magnetoresistive (AMR) effect and a firstelectrode on a first side of the tunneling barrier layer, a secondelectrode on a second side of the tunneling barrier layer, and first andsecond contact sets on the first side of the tunneling barrier, whereinthe first electrode exhibits an AMR effect; accessing a first sensorconfiguration of the TMR stack by the first contact set to measure acurrent-in-plane (CIP) TMR effect; accessing a second sensorconfiguration of the TMR stack by the second contact set to measure anAMR effect, the second contact set having a contact distance smallerthan a contact distance of the first contact set; and using the CIP TMReffect and AMR effect to determine a 360-degree unique magnetic fieldangle.
 28. The method of claim 27, wherein using the CIP TMR effect andAMR effect to determine a 360-degree unique magnetic field angle furthercomprises: determining a higher precision 180-degree unique magneticfield angle from the AMR effect; and determining a lower precisionhalf-space of the magnetic field angle from the CIP TMR effect.
 29. Anangle sensor for measuring an external magnetic field with 360 degreesof uniqueness comprising: a tunneling magnetoresistive (TMR) stackhaving a tunneling barrier layer, a layer exhibiting an anisotropicmagnetoresistive (AMR) effect and a first electrode on a first side ofthe tunneling barrier layer, a second electrode on a second side of thetunneling barrier layer, a first contact set comprising contacts on thefirst and second sides of the tunneling barrier layer, and a secondcontact set on the first side of the tunneling barrier layer, whereinthe first electrode exhibits an AMR effect; wherein the TMR stack has afirst sensor configuration when the first contact set is used and asecond sensor configuration when the second contact set is used, thefirst and second contact sets having different contact distances.